May 7, 2014

Dust is everywhere on Mars, and plays a key role in the red planet’s weather, according to a Texas A&M University researcher who has spent much of the past decade observing the phenomenon.

Mark Lemmon, associate professor of atmospheric sciences at Texas A&M, has served as a camera operator on numerous Mars missions, especially those involving the Mars exploration rovers Spirit and Opportunity. Spirit landed in 2004 and transmitted thousands of images back to Earth before it quietly expired in 2010. However, Opportunity is still sending back plenty of images, said Lemmon, who has published his findings describing 9 years of dusty weather on Mars in the current issue of the journal Icarus.

Lemmon, who helps operate the rovers’ cameras, said the solar-powered Spirit and Opportunity have gone above and beyond the call of duty.

The rovers were expected to last only about 90 “sols,” but worked for far longer. A “sol” is one day on Mars, or 24 hours and 39 minutes.

“The fact that Spirit lasted over six years, while Opportunity is still going strong is nothing short of amazing,” Lemmon told the TAMU Times.

“Their longevity exceeded any and all expectations. Together, they have sent back more than 300,000 images and given us information about Mars that we simply would never have known without them.”

The photographs sent back by the rovers include many images of the Martian terrain and weather, which is extreme by any standard.

Even at the “tropical” sites visited by the rovers, Mars’ weather is dominated by dusty skies and intense storm seasons when the planet is close to the sun, and brutal temperatures when it is the farthest from the sun, Lemmon said.

The reduced solar power during these times restricted the operation of the twin rovers, Lemmon said.

“The rovers use the sun to keep track of the dust. As the dust levels rise and fall, the sun’s brightness in images does, too. And during storms, the sun can get quite dim, only a small percent of its brightness is seen during clear weather,” he added

Since the rovers are dependent on sunlight that permeates the Martian atmosphere, operations had to be suspended during these times.

Spirit stopped communicating in the Martian winter of 2010 when so much dust covered the solar panels that it had no power whatsoever.

Dust levels on the panels are checked every sol at 11 a.m., and “when we do, we can see the seasonal pattern of the sun’s motion, which is called an analemma. An analemma on Earth shows the Earth’s axial tilt, which gives us our four seasons. On Earth, an analemma looks like a figure 8, but on Mars, it looks like a teardrop,” Lemmon said.

The analemma shows the intense dust storms that pummeled the rovers, including one in 2007 that halted communications to Earth for several days. The broad turn of the analemma shows the fading sun on Mars.

Interestingly, although Mars is known as the Red Planet, the rovers beamed back images showing a typical Martian sunset that is usually blue, Lemmon said.

“We have known since the 1970s that Martian sunsets tend to be blue, but recent images vividly show Martian sunsets,” he explained.

“The combination of dust particles and atmospheric conditions on Mars makes for some unusual sunset colors, but do not yield the spectacular sunsets we sometimes see on Earth.”

Lemmons’ NASA-funded project was conducted as part of his role as a member of the Athena science team that directs the rovers. Some of the images were selected to be displayed in the Smithsonian’s Air and Space Museum exhibit, “Spirit & Opportunity: 10 Years Roving Across Mars.”